1. Field of the Invention
The present invention relates to a developing apparatus having a developer carrying member and a developer regulating member, and more particularly to a developing apparatus adapted for use in an image forming apparatus utilizing an electrophotographic process or an electrostatic recording process such as a copying apparatus, a printer, a facsimile apparatus, etc.
2. Description of the Related Art
In an image forming apparatus of electrophotographic process, a recorded image is formed by charging an image bearing member, then exposing it according to image information to form an electrostatic image, supplying the image bearing member with a developer according to such electrostatic image thereby forming a developer image, then transferring such a developer image by transfer means onto a recording material (transfer member) such as a recording sheet, an OHP sheet or a cloth, and fixing it by fixing means.
There is already known an image forming apparatus for example utilizing, as charging means, contact charging means which is maintained in contact with the image bearing member, and, as developing means, non-magnetic one-component contact developing means. FIG. 7 is a schematic cross-sectional view of principal portions of such conventional image forming apparatus 300.
The image forming apparatus 300 is provided with a drum-shaped electrophotographic photosensitive member (hereinafter called “photosensitive drum”) 10 as an image bearing member. The surface of the photosensitive drum 10 is uniformly charged by applying a predetermined charging bias to a charging roller 11, serving as charging means which is in contact with and driven by the surface of the photosensitive drum 10. Then the surface of the photosensitive drum 10 is exposed, by an exposure apparatus 12, to a light L corresponding to an image information signal, thereby forming an electrostatic latent image.
The electrostatic latent image formed on the photosensitive drum 10 is supplied with a toner serving as developer, by a developing apparatus 13 serving as developing means and including, in a developing container 20, a developing roller 16 which is a roller-shaped developer carrying member, a developing blade 17 which is a blade-shaped regulating member, and a toner supply roller 18 which is a developer supplying member, whereby the latent image is rendered visible as a developer image (toner image).
Then, in a transfer portion N, a transfer bias is applied to a transfer roller 26 constituting transfer means, whereby the toner image formed on the photosensitive drum 10 is transferred onto a recording material P, supplied from a recording material supply portion 40 equipped with a recording material cassette 41, a recording material supply roller 42 serving as conveying means etc., thereby forming an unfixed image. Then the recording material P is conveyed to a fixing apparatus 30 in which the unfixed image is fixed to the recording material P, and is thereafter discharged to a sheet discharge tray 35 whereupon the image formation is terminated.
Transfer residual toner, which has not been transferred but remains on the photosensitive drum 10, is recovered by a cleaning blade 14 constituting cleaning means into a waste toner container 15. Thus the photosensitive drum 10 is cleaned and is used for image formation repeatedly.
On the other hand, particularly in a conventional contact developing method (in which a developing roller is in contact with an image bearing member at the image development), because of a high developing selectivity, toner of higher developing property on the developing roller 16 is preferentially used for the development in the developing step, so that toner of inferior developing property remains in the developing container 20. When a remaining amount of the toner is reduced, the toner in the developing container 20 shows an increase in the proportion of the toner of inferior developing property and causes deterioration of the toner itself, thereby resulting in an increased fogging in a latter part of a printing durability test, a decrease in the transfer efficiency in an image of a halftone pattern, or in a so-called white-spots-image caused by defective transfer in many small areas on an image.
Therefore, as described in Japanese Patent Application Laid-open No. 2000-227695, in an image forming apparatus having rotary development means, the toner of inferior developing property is forcedly consumed for example by providing forced consumption means which causes a forced consumption of a toner layer sticking to the external periphery of the developing roller 16 in a final stage of an operation for optimizing the developing conditions, or by forming a solid image of a high coverage rate (image of maximum density) by executing a charging of the photosensitive drum 10, an exposure thereof and a development and recovering the toner into the waste toner container 15 without being transferred to the recording material P, at every predetermined number of prints.
However, even with such forced toner consumption by the solid image printing at every predetermined number of prints, the toner of inferior developing property may still not be transferred onto the photosensitive drum 10 but remain on the developing roller 10 in the developing step, so that the toner of inferior developing property cannot be sufficiently transferred to the photosensitive drum 10 thereby resulting in an increase of fogging in a latter part of the service life of the developing apparatus or a white-spots-image in a halftone patterned image.
Furthermore, in a latter part of the service life of the developing apparatus, there are sometimes observed a black-lined image caused by a fusion-bonding of deteriorated toner on the developing blade 17, an increase of fogging caused by a fusion-bonding of toner on the developing roller 16, and a white-spots-image in a halftone patterned image.